With reference to FIG. 1 of the drawings, the reference numeral 10 generally designates a cross-section of soil which has been contaminated with a water soluble contaminant. One such contaminant may be produced water from oil field operations, which water may contain brine and other water soluble contaminants. The soil 10 is comprised of surface soil 12 having a thickness of about six to twenty-four inches, and subsoil 14 which lies beneath the surface soil. A portion of the interface between the surface soil 12 and the subsoil 14 is identified by the reference numeral 2. As shown in FIG. 2 in an enlargement of the portion 2 of the soil 10, the surface soil 12 and the subsoil 14 each comprise soil particles 16 naturally arranged so as to define relatively large macropores 18, and relatively small capillary pores 20 which constitute a continuum extending between the surface soil and the subsoil.
When the soil 10 is saturated with water (i.e., the macropores 18 are filled with water, not shown), for example, after irrigation or precipitation such as natural rainfall, water migrates downwardly from the surface soil 12 primarily through the macropores 18 into the subsoil 14, as indicated by the arrow 22 in FIG. 1. If dissolved contaminants (not shown) such as salts, acids, bases, metals, organic substances, and the like are in the surface soil 12, then the contaminants are carried by the water into, or through, the subsoil 14 where the contaminants have little effect on vegetation (not shown) that may be present in the surface soil.
During dry periods, when evaporation and transpiration rates exceed precipitation rates, water evaporates and transpires from the surface soil 12, leaving the surface soil dryer than the subsoil 14. Under these types of unsaturated conditions (i.e., when the macropores 18 contain air instead of water) water may migrate upwardly from the subsoil 14 through the continuum of capillary pores 20 to the surface soil 12, as indicated by the arrow 24 in FIG. 1, rather than downwardly through the macropores 18, as indicated by the arrow 22 in FIG. 1. Dissolved contaminants in the subsoil 14 are then carried upwardly with the water into the surface soil 12, where the water evaporates, resulting in an accumulation and increased concentration of contaminants in the surface soil. The presence of such contaminants in the surface soil 12 inhibits the growth of vegetation and accelerates erosion of the soil and is, accordingly, detrimental to a number of different land management schemes, including agriculture, oil and gas production, mining, land farming, highway right-of-way management, and the like.
Barriers may be created to prevent the upward capillary migration of water and dissolved contaminants in unsaturated soil. The most common type of barrier utilized comprises a layer of clean gravel 26, with very few fines, positioned in the soil 10, as depicted in FIG. 3, at a selected depth and generally substantially between the surface soil 12 and the subsoil 14. Because the gravel 26 does not include capillary pores necessary to sustain the unsaturated migration of water from the subsoil 14 to the surface soil 12, the continuity of capillary pores 20 necessary to sustain capillary migration of water in the soil 10 is broken. Therefore, water and contaminants in the subsoil 14 cannot migrate upwardly from the subsoil 14 through the capillary pores 20 to the surface soil 12, as indicated by the shortened arrow 24a. Water and contaminants can, however, continue to migrate downwardly from the surface soil 12 through the gravel barrier 26 to the subsoil 14, as indicated by the arrow 22. Gravel barriers have a number of drawbacks. For example, gravel barriers require a poorly-graded gravel with minimal fines to be effective and, furthermore, are usually economically and technically impractical for soil remediation. Additionally, if it is ever desirable to remove the gravel barrier, such removal is even more economically and technically impractical than laying the barrier.
Therefore, what is needed is an economic and practical system and method for creating a barrier that prevents the upward capillary migration of contaminants in soil, and that is readily removable.